Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$5.30	3.675%	$5.4948	$5.49	$5.50	$5.50
Purchase #2	$133.55	6.241%	$141.8849	$141.88	$141.90	$141.90
Purchase #3	$68.70	4.754%	$71.966	$71.97	$71.95	$72.00
Purchase #4	$54.27	10.763%	$60.1111	$60.11	$60.10	$60.10
Purchase #5	$40.87	10.211%	$45.0432	$45.04	$45.05	$45.00
Purchase #6	$121.84	10.113%	$134.1617	$134.16	$134.15	$134.20
Purchase #7	$185.42	12.606%	$208.794	$208.79	$208.80	$208.80
7 purchase totals =	$609.95		$667.4557	$667.44	$667.45	$667.50